title: Intraocular lens power calculation by ray-tracing after myopic excimer laser surgery.
abstract: OBJECTIVE
  To investigate the refractive outcomes of intraocular lens (IOL) power calculation by ray-tracing after myopic excimer laser surgery.
  
  
  METHODS
  Prospective, interventional case series.
  
  
  METHODS
  setting: Multicenter study. participants: Twenty-one eyes of 21 patients undergoing phacoemulsification and IOL implantation after myopic laser in situ keratomileusis or photorefractive keratectomy were enrolled. intervention: IOL power calculation was performed using internal software of a Scheimpflug camera combined with a Placido disc corneal topographer (Sirius; CSO). Exact ray-tracing was carried out after the axial length (measured either by immersion ultrasound biometry or partial coherence interferometry), target refraction, and pupil size had been entered. main outcome measures: Median absolute error, mean absolute error, and mean arithmetic error in refraction prediction, that is, the difference between the expected refraction (as calculated by the software) and the actual refraction 1 month after surgery.
  
  
  RESULTS
  The mean postoperative refraction was -0.43 ± 1.08 diopters (D), with a range between -1.28 and 0.85 D. The mean arithmetic error was -0.13 ± 0.49 D. The median and mean absolute errors were +0.25 D and 0.36 D, respectively. Also, 71.4% of the eyes were within ± 0.50 D of the predicted refraction, 85.7% were within ± 1.00 D, and 100% within ± 1.50 D.
  
  
  CONCLUSIONS
  Ray-tracing can calculate IOL power accurately in eyes with prior myopic laser in situ keratomileusis and photorefractive keratectomy, with no need for preoperative data.
authors.affiliation: Giovanni Battista Bietti Foundation, Istituto di Ricerca e Cura a Carattere Scientifico, Rome, Italy. Electronic address: giacomo.savini@alice.it.
authors.forename: Giacomo
authors.initials: G
authors.lastname: Savini
authors.affiliation: Casa di Cura San Camillo, Forte dei Marmi, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Bedei
authors.affiliation: Studio Oculistico d'Azeglio, Bologna, Italy.
authors.forename: Piero
authors.initials: P
authors.lastname: Barboni
authors.affiliation: Giovanni Battista Bietti Foundation, Istituto di Ricerca e Cura a Carattere Scientifico, Rome, Italy.
authors.forename: Pietro
authors.initials: P
authors.lastname: Ducoli
authors.affiliation: Jules Stein Eye Institute, University of California, Los Angeles, Los Angeles, California, and St. Mary's Eye Center, Santa Monica, California.
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Hoffer
mesh_terms: D001699:Biometry; D005260:Female; D006801:Humans; D007368:Interferometry; D020731:Keratomileusis, Laser In Situ; D054018:Lasers, Excimer / Q000627:therapeutic use*; D019654:Lens Implantation, Intraocular; D007910:Lenses, Intraocular; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000601:surgery*; D055095:Optics and Photonics; D018918:Phacoemulsification; D011182:Postoperative Care; D011446:Prospective Studies; D012029:Refraction, Ocular / Q000502:physiology; D014792:Visual Acuity / Q000502:physiology